1. field of the Invention PA1 2. Description of the Prior Art
The present invention generally relates to a pump jack and more particularly a hydraulically operated pump jack for oil wells, and the like, for more effectively pumping oil by utilizing a relatively small horse power prime mover, a hydraulic pump with reversing valve and cushioning means associated with the hydraulic pump and hydraulically operated piston and cylinder assembly for controlling the pivotal movement of the walking beam in a manner to prolong the life expectancy of the components and pump a predetermined capacity of oil at a lower operating and maintenance cost.
Oil well pump jacks have been in use for many years and usually include a pivotal walking beam supported from a stanchion or samson post by a saddle bearing with the end of the beam overlying the oil well having a horsehead thereon to which a wire rope or cable bail assembly is connected for securing the beam to the upper end of a polish rod for reciprocating the polish rod, sucker rods and downhold pump. The walking beam is driven by pitman rods or arms which in turn are connected to eccentric cranks on a crank shaft with counterbalance devices being associated with the mechanism. While such devices have performed, they are relatively expensive and heavy in weight due to the large reduction gear unit and counterbalance unit normally employed. Previously known devices of this type require substantial maintenance time in order to retain the components in properly adjusted position and proper operating condition. Also, in view of the mechanical nature of the known pump jacks, substantial forces are exerted on the components of the pump jack as well as the components of the oil well pump itself which has resulted in excessive wear and fatigue breakage of various components. Efforts have been made to utilize fluid pressure operating mechanisms for pump jacks. Ross U.S. Pat. Nos. 3,221,568 and 3,405,605 and Kelley U.S. Pat. No. 3,971,213 illustrate efforts to utilize hydraulic piston and cylinder assemblies and pneumatic piston and cylinder assemblies for operating the pump jack.